The present invention relates to a mechanism for migrating data (record) contents from one recording medium to another over generations in a readable manner, and providing the data contents from a current recording medium.
Data stored in a storage device is required to be readable in long-term archiving over ten years or longer. An example of a typical tape drive for archiving data includes a Linear Tape-Open (LTO) tape drive, the IBM enterprise tape drive TS1130, and the like. Further, even after hardware such as a recording medium or a device for storing data is changed to a new one, the stored data needs to he readable from a current medium by being migrated to the current medium.
Migration between recording media is an unavoidable problem in archiving data in a storage system. The migration can roughly be divided into two categories. One is migration explicitly performed by an application having recorded data in the storage system. In the migration explicitly performed by an application having recorded data in a storage system, a server on which the application operates bears a large load. The other category is migration (serverless migration) performed irrespective of an application having recorded data in the storage system. The serverless migration is preferable in that the data recording application does not require a migration function and load on the server can be distributed.
Steps 1 to 3 below show a basic flow of the serverless migration:                1. An application X (a general application using a storage system) stores data in a recording medium A.        2. An application Y (an application dedicatedly performing migration) monitors states (a use period, a frequency of a recoverable error, and the like) of the recording medium A. When determining that the life of the recording medium A will reach an end of its lifespan soon, the application Y migrates data stored in the recording medium A to a recording medium B and then discards the recording medium A. The application Y stores correspondence (recording media migration information) between the recording media A and B in a database (DB) or the like.        3. When the application X requests access to the recording medium A, virtualization is performed to allow the application X to access the desired information in the recording medium B on the basis of recording media migration information stored in the DB, or the like, in Step 2. The migration is naturally performed multiple times depending on the storage periods of data in the recording media.        
In a migration process in long-term archiving, the data stored by the application X migrates from recording media A to D through media B and C. Recording media before and after migration do not necessarily have a one-to-one relationship. Data stored in multiple first-generation recording media may be migrated to a single next- or current-generation recording medium. In addition, data stored in a single recording medium may be divided and recorded in multiple recording media or recorded in multiple recording media in an overlapping manner.
One of problems of the present serverless migration is that recording media migration information stored in a DB or the like might be lost. In such a case, even though target data is present in the recording medium B, there is no way to know that the data that has been recorded in the recording medium A by the application X is already migrated to the recording medium B. The problem is that the application X consequently cannot access the target data.
For example, Japanese Patent Application Publication No. 2002-216458 describes a mechanism in which disk management information is stored in a recording medium, and the recording medium is managed based on the management information. The mechanism described in Japanese Patent Application Publication No. 2002-216458, however, provides no description of any mechanism for holding and utilizing meta information in data migration. When a database including migration information is lost in a conventional system environment in which data is read from an archive medium, it is laborious to rebuild the archive data readable environment.